Fusible protective device for electric circuits



Aug. 5, 194%- .J. A. MCENTEE FUSIBLE PROTECTIVE DEVICE FOR ELECTRICCIRCUITS Filed Jan.

Patented Aug. 6, 1940 UNITED STATES PATENT OFFICE FUSIBLE PROTECTIVEDEVICE Eon ELECTRIC cmcUrrs setts Applicationdanuary 22, 1936, SerialNo. 60,239

31 Claims.

This invention relates to fusible protective device for electriccircuits.

It is. common practiceto protect electric circuit and the apparatustherein against damage due to overloads by fuses which are in the serieswith the circuit and are adapted to blow when traversed by a current insubstantial excess of their rated continuous carrying capacity. Forcircuits of moderate current carrying capacity, as say up to andincluding 30 amperes, the fuses are commonly of the screw plug type.Electric circuits, and many pieces of apparatus operated from thecircuits, are able to carry a moderate overload current for aconsiderable period of time normal current is demanded for a shortperiod of time. For instance, an electric motor that is adapted to beconnected directly to the line without the use of a starting impedancedraws for a second or so or until the motor comes up to normal speed, astarting current that may be from five to ten times in excess of itsnormal full load running current.- An electric fuse and particularly oneof the plug type, having a capacity suited to the normal current,ordinarily is unable to carry the momentary overload and thus blows andinterrupts the circuit needlessly.

.Hence an object of the present invention is the provision of animproved form of a fusible protective device and particularly one of thescrew plug characterized by its ability to carry a current that isconsiderably in excess of its normal rated current for a substantialperiod of time sufllcient topermit excessive current momentarily to besupplied to the circuit and the apparatus therein and yet to operatetointerruptthe circuit if excessive current flow persists for an unusualtime and also if the normal current is exceeded for a longer time.

A further object of the invention is, the provision of an improved formof fusible protective device having means providing for the delayedinterruption of the circuit when traversed by a moderate overlo currentand the quicker or instant interruptio of the circuit when traversed bya short-circuit current.

The fusible protective device embodying the present invention includes anormally solid mass of readily fusible metal adapted to be heated to thefusing point by an electric resistance element and when solidretaining-therein the spring tensioned end of a movable conductingmember and when fused releasing its hold upon the conducting member,thereby permitting the spring to without damage; and inthe operation ofmany pieces of apparatus a considerably higher than withdraw the ehd ofthe member from engagement with the fused mass and thereby interrupt thecircuit.

An object of the present invention is the provision of novel means forholding the fusible metal mass, the holding means being a part of theheating element.

A yet further object is the provision of holding means for the fusiblemass wherein the heating element is a resistance conductor wound in ahelix, the fusible mass being contained in one end of the helix bydirect engagement with the convolutions thereof.

Another object of the invention is the provision of a fusible protectivedevice of the type above described having a construction wherein the operative elements can be contained within a screw plug body thedimensions of which, and particularlythe length of which, does notexceed the ,dimensions of the ordinary plug type of fuse so that thedevice can go in any receptacle and in any installation having a plugfuse, to replace the fuse.

A further object of the invention is the provision of a fusibleprotective device of the screw plug type having a novel form of springfor mov- ,ing the conductor.out of the fused fusible mass whereby arelatively great separation is provided between the conductor and themetal mass for a smaller movement of the spring and also V wherein thelength of the device can be kept and permitting a'long circuitinterrupting gap.

Another object is generally to improve the construction and operation offusible protective de-- vicesv for electric circuits.

- Fig. 1 15.8. side elevation of the fusible protective device embodyingthe present invention.

Fig, 2 is a sectional elevation of the device'of Fig.1 taken along line2-4 of Fig. 1.

Fig. 3 is a plan view of the device of Fig. 1 1,

the cap and transparent window being removed.

Fig. 4 is a section taken along the line H of Fig. 2.

Fig. 5 is a sectional detail similar to Fig. 4 but illustrating theoperated position of the parts.

Fig. 6 is a sectional detail taken along line 6-6 of Fig. 5.

wardly projecting boss It in which a. center contact 58 is fixed, thestem or shank 2d of the center contact having an internal recess 22.

The plug body is provided with an internal open-top chamber 2% in whichthe operative parts of the device are located; The top of the body isprovided with a peripherally outstanding flange 25. An electricallyinsulating transparent disc 28 of suitable material, as mica, overliesthe top of the body and is seated upon the flange 2S and constitutes aclosure for the open end offthe chamber 2d. A metal disc-retaining cap38 has its topwall 32 overlying and seated upon the transparent disc 28and its side wall 3% engaged with the outer face of the flange 28 andthe end of the side wall turned in under the flange andtherebypermanently retained tightly engaged (with the plug body. The top wall32 of the cap is provided with an opening or window 36 through which aview of the interior of the plug chamber can behad. The plug body so fardescribed is essentially the body of a plug type of fuse and has thesame dimensions.

A' combined holder and heating element for a mass of readily fusiblemetal is located in the .bottom part of the chamber 25. Said holder andheating element comprises a helix 38 of resistance wire 60, thelower end$2 of the resistance wire being extended parallel with the axis of thehelix and located in the recess 22 of the shank of the end cap where itis permanently retained by a mass of solder having a melting pointsufliciently high to remain solid at any temperature sumcient to meltthe readily fusible metal and cause the operation of the. device.

The uppermost two or three turns 36 of the helix are in substantialcontact or at least are sufiiciently close to one another to form a cupto retain a mass 58 of readily fusible metal. The cupis provided with abottom by a plate dd of suitable heat resistant sheet material, asmica,for instance, which is inserted between and is gripped by theconvolutions under the fusible mass. The convolutions below the cup areseparated and constitute a heating coil which when traversed bysufiicient current heats the readily fusible metal mass 48 in the cupand ultimately causes it to melt or fuse.

' While the bottom plate 59, as above described,

is intended to be a permanent part of the cup,

its presence in the completed device is not essential. The plate may beretained in place while the molten metal is poured into the cup anduntil the metal mass has solidified. It can then be removed. Such aconstruction is illustratedin Fig. 7. For this purpose the plate can beof mica, aluminum or other sheet material not harmed by the heat of themolten metal mass or adapted tobond therewith. t

The fusible metal mass is normally connected to the terminal shell idthrough a flexible conducting strip 5% which preferably is composed ofcopper although it can be composed of fuse link material, usually zinc.The inner end 56 of the strip is imbedded in the normally solid metalmass 448 and is thereby held in electrical and mechanicalengagement'with the metal mass. and is anchored thereby. The outer end55 of the strip islocated in a channel 58 formed in the I &

wall o the body it and is imbedded in a mass 66 of solder by which it isconnected electrically with the terminal shell 5. The strip is thus oflooped or inverted U formation. The strip is under spring tension actingin such manner as 10 to constantly act upon the inner end .55 of thestrip to pull it upwardly out of engagement with the fusible metal mass68 when said mass be; comes fused.

The spring tension is provided with a how 15 spring 62 consisting of anormally straight helix of spring wire wound in close convolutions. Thespring helix is extended transversely across the chamber 2% of the plugbody under the conducting strip 52, and the ends of the spring helix 20are receivedin notches 5d formed in'the side wall of the plug bodyimmediately under the transparent cover 253. Barriers 56 integral withthe plug body traverse the ends of the notches to isolate the ends ofthe spring helix from the 25 metal cap 3!). The diameter of the springhelix and the depth of the notches 56, however, preferably is such thatthe'helix projects slightly above the tops of the notches so that themica disc 28 is pressed firmly thereagainst by the 30 metal cap wherebyto grip the ends of the spring helix between the mica disc and thebottoms of the slots so asto prevent endwise movements of the spring.

The conducting strip 52 is looped over thejg middle part of thespringhelix and the length of the strip is such that in the normal conditionof the device the spring helix is bowed downwardly by a substantialamount as indicated in Figs. 2 and 4, thereby placing the conductingstrip (30 under a tension in a direction to withdraw the inner end ofthe strip out of the fusible metal In the assembly of the device thefollowing procedure is convenient. The ends of the conducting strip aresecured to the solder masses 58 and fifl'with the strip forming an ustanding loop, as shown. A curved wire or nee e is then run through theinitially straight spring 62,

thereby forming it into the bow shape illustrated.

The spring on the needle is then passed under the looped strip 52 andtheends of the spring located in the. notches E i. The needle is thenwithdrawn out of the spring and thespring flexes upwardly somewhat andapplies tension 55 on the strip 52, the ends of the spring bearingdownwardly on the bottoms of the notches and projecting upwardly partlyabove the top face of the plug body Hi. The mica disc 28and end 'cap 30are then applied, bending the upstanding spring ends downwardlyandclamping them in place. The clamping action is desirableforpreventing endwise movement-of the spring especially if the walls of thenotches are omitted but is not necessary merely to retain the spring 65ends in the notches. 4

Y Under normal conditions of service, where the device is traversed bynot more than the'current which it can carry continuously-the parts remain in the aforesaid relation. When, however,

the device is subjected for a sufficient period of time to an excessivecurrent the heat generated by the heating element 38 raises thetemperature of the readily fusible metal mass tdthe melting pointthereof.v The metal mass thus becomes fluid and no longer can retain itsgrip on the inner end of the conducting strip 52. The inner end of thestrip is thereupon pulled rapidly upward out of the fusible mass by thetension of the bow spring 62, thereby interrupting the circuit, the bowspring usually assuming a straight horizontal position as illustrated inFig. 5.

Due to the arrangement of the spring under and in engagement with thelooped portion of the conducting strip and to the fact that there is arelative-movement between the strip and the spring in the direction ofthe length of the strip,

the upward movement of the inner end of the conducting strip is twicethat of the upward movement of the spring, per se. Due also to theinherent rigidity of the free end of the conducting strip said end ismoved upwardly into a position where it lies against the inner face ofthe mica disc 28 as illustrated in Fig. 6. Thus a very large distance ofseparation between the strip and the fusible metal mass is attainedwithout the necessity for a long length of enclosing casing.

The conducting strip 52 is preferably provided with a more readilyfusible portion, or fusing zone by having a part of reducedcross-section as made by the perforation 68 located in the inner end ofthe conducting strip in'a position to be out of the mass of readilyfusible metal when the device is in service condition. They can-vaporizemore or less completely without the generation of harmful gas pressureswithin the enclosing casing. For currents of lesser magnitude but stillsufficient to fuse the strip before the readily fusible metal 'melts,the strip will fuse at its portion of highest temperature, usuallybetweenthe spring 62 and the mass of fusible metal 48, which portion isthus the equivalent of the more readily fusible portion provided by' theperforation.

I claim:

1..A fusible protective device comprising a. fusible mass, heating meansfor melting said mass, a fusible conductor having an end engaged withand anchored by said mass and adapted to be released upon the fusing ofsaid mass, terminals, said conductor, heating means and fusible massbeing in series with said terminals, said conductor having a partadapted to fusewhen traversed by a dangerous current,

and spring means operatively excluded from the circuit between saidterminals tensioning said conductor at said fusible mass and also atsaid fusing part.

- 21. A fusible protective device comprising a fusible mass, heatingmeans therefor, a fusible conductor having one anchored end and itsother end engaged with and anchored by said mass, terminals betweenwhich said mass, heating means and conductor areconnected in series,said conductor having a fusing section, and spring means operativelyexcluded from the circuit between said terminals engaged with and actingon said condubtor intermediate its ends in a direc: tion that tensionssaid conductor at said fusible mass a d also at said fusing section.

3. In a fusible protective device having a fusible mass, a conductorengaged with and anchored by said fusible mass, and spring means towithdraw said conductor from the molten fusible mass, the combinationtherewith of a holder for the fusible mass comprising a helix havingconvolutions directly engaged with and within which the fusible mass isdisposed,

4. In a fusible protective device having a fusiblemass, a conductorengaged with and anchored by said fusible mass, spring means to withdrawsaid conductor from the molten fusible mass, the combination therewithof a holder for the fusible mass comprising a helix having closeconvolutions directly engaged with and within which the fusible mass isdisposed.

5. In a fusible protective device having a fusible mass, aconductorengaged with and anchored by said fusible mass, spring means to withdrawsaid conductor from the molten fusible mass, the combinationtherewith'of a holder for the fusible mass comprising a helix havingclose convolutions directly engaged with and within which the fusiblemass is disposed, and a bottom closure member traversing the helix undersaid fusiconvolutions directly engaged with and within which the fusiblemass is disposed, and a bottom closure member traversing the helix undersai I fusible mass and located between the convolu tions of the helix,the convolutions on opposite sides of said closure member being inpressure engagement therewith. 7. In a fusible protective device havinga fusible mass, a conductor engaged with and anchored heating coil forsaid fusible mass having some of its convolutions surrounding anddirectly engaged with said fusible mass and forming a retaining cuptherefor.

8. In a fusible protective device having a fusible mass, a conductorengaged with and anchored by said fusible mass, and spring means towithdraw said conductor from the molten fusible mass, the combinationtherewith of a holder and electric heating element for said fusible masscomprising a resistance helix having said fusible mass retained thereinby direct engagement with convolutions-of said helix which form aretaining cup for said fusible mass.

9. In a fusible'protective device having a fusible mass, a conductorengaged with and anchored by said fusible mass, and spring means towithdraw said conductor from the molten fusibleby said fusible mass,spring means to vvitluirawv said conductor from the molten fusible mass,the

combination therewith 'of a holder and electric heating element forsaid. fusible mass comprising plug body having a center contact. ascrewa resistance helixhaving -a series of open convolutions and aseries of close convolutions, said fusible mass being contained withinand engaged with said close convolutions, and a closure-membertraversing said helix under said fusible mass.

11. A fusible protective device comprising an electric resistance helix,a fusible mass contained in one end of said helix and retained-thereinby ing close convolutions at one end surrounding and directly engagingsaid fusible mass, and a closure plate-traversing said helix under saidfusiblemass. 4

13; A fusible protective device comprising a threaded shell and aninternal chamber, a heating element comprising a resistance helix insaid chamber having an end connected with said center contact, a fusiblemass retained in the other end of said helix by direct engagement withconvolutions thereof, a conductor having one end engaged with andanchored by said fusible mass and its other end connected with saidshell, and spring means for withdrawing said conductor from said fusiblemass;

14. A fusible protective device comprising a fusible mass, a conductorforming a part of the circuit through said device engaged with andanchored by said fusible mass,spring means for withdrawing saidconductor from said fusible mass, 7 and means for supporting said springmeans for flexure transversely of its length; said spring means bearingon and disposed with its length transversely of the length'of saidconductor. r

15. A fusible protective device comprising a fusiblemass, a conductorforming a part of the circuit through said device engaged with andanchored by said fusible mass, and ineans including a bow spring actingo said'conductor for withdrawing it from said sible mass.

16. A fusible protective device comprising a] fusible mass, a conductorengaged with and'anchored by saidfusible mass, and means having adetermined distance of action for withdrawing said conductor a greaterdistance from said fusible mass.

17. A fusible protective device comprising a fusible mass, aconductorforming a part of the circuit through said device engaged with andanchored by saidfusible mass, and a bow spring for withdrawing saidconductor from said fusible mass, said bow springv being disposedcross-wise ofsaid conductor in engagement therewith.

18. A fusible protective device comprising a fusible mass, a conductorhaving a fixed endand an end anchored by said fusible mass, and a bowspring disposed-cross-wise of said conductor and acting thereonintermediate the ends thereof.

19. A fusible protective device comprising a fusible mass, a conductorhaving a fixed end and an end anchored by said fusible mass, and a bowspring comprising a springhelix disposed crosswise of said conductor andacting thereon intermediate the ends thereof. I

. 20. A fusible protective device comprising a fusible mass, a conductorhaving a fixed end and an end anchored by said fusible mass, a bowspring comprising a spring helix disposed crosswise of said conductorand acting thereon intermediate the ends thereof, and a support for theends of said helix.

.21. A fusible protective device comprising a fusible mass, a loopedconductor having a fixed end and an end anchored by said fusible mass,and a spring helix disposed cross-wise of said conductor in the loopthereof and bearing there? against.

22. A fusible protective device comprising a fusible mass, a loopedconductor having a fixed end and an end anchored by said fusible mass, aspring having a part disposed cross-wise of said conductor in the loopthereof and bearing thereagainst, and an anchorage for said spring.

23. A fusible protective device comprising an enclosing casing havingterminals, 2. fusible mass connected with one terminal, a conductorcon-=- nected between said fusible mass and said other terminal, and aspring helix extended cross-wise of and'bearing against said conductorbetween the ends thereof;

24. A fusible protective device comprising a plug body having a centercontact and ascreivthreaded'shell, a fusible mass connected with saidcenter contact, a loop conductor having one end releasabl'y anchored bysaid fusible mass and its other end connected-with said shell, and aspring having a part extended transversely of said conductorand hearingon the loop part thereof.

25. A fusible protective device comprising a plug body having acentercontact'and a screwthreaded shell, a fusible mass connected with saidcenter contact, a, looped conductor having] one end releasably anchoredby said fusible mass and its other end connected with said shell, and atensioned spring helix disposed cross-wise of said 5 conductor andbearing on the loop thereof.

26. A fusible protective device comprising a fusible mass, a conductorhaving a fixed end, and

an end releasably anchored by said fusible ma and spring means having apart extended transversely of and bearing on said conductor andtensioning the entire conductor between its ends.-

27. A fusible protective device comprising a casing having a-chainber, aspring helix travers-= ing said chamber and having its ends supported bythe wall of said chamber, a conductor extended across said helix andbearing thereagainst, and

a fusible -mass relea'sably anchoring the end of said conductor.

28. A fusible protective device comprising-a cas-.

ing having a chamber, a center contact and a screw-threaded shellcarried by said casing, a.

spring helix traversing said chamber and having its ends supported bysaid casing, a conductor having'an end connected to said shell andextended across 'and'bearing against said helix,

and a fusible mass connected with said center contact and releasablyretaining'the other end of said conductor. I

- 29..A fusible protective device comprising a casing havingaan openended chamber, a transparent insulating member traversing the open endof said chamber,.means for retaining said transparent member in place, acenter contact at the bottom of said 0, a screw-threaded shell.-

surrounding said casing, a spring helix extended across said chamberunder said transparent member and having its ends supported by saidcasing, a conductor having an end connected with said shell and extendedacross and bearing against said helix, and a fusible mass connected withsaid center contact releasably retaining the other end of saidconductor.

30. A fusible protective device comprising a resistanse heating elementhaving a supported end and a free end, a fusible mass carried by one endof said element, a terminal connected with the other end of saidelement, a conductor having one end releasably'anchored by said fusiblemass and having a fusing part, a second terminal connected with theother end of said conductor, and spring means exerting tension on saidconductor and said fusing part thereof.

31. A fusible protective device comprising an r enclosing casing havinga window, a fusible mass 5 within said casing, current responsive meansfor fusing said mass, a flexible conductor engaged with and normallyanchored by said mass in a position remote from said window, and meansunder said conductor for withdrawing said conductor from the fused massand for flexing it into position displaying the freed end thereofclosely adjacent said window.

JAMES A. MCENTEE.

e CERTIFICATE OF comc'rion. Potent no. "2,210,05 6.

. August 6, 191m. JAHES-A.-H0EN1EE.

It ro er 2y certified that error appears in the printed apecf Lficationor the above numberedpatent requiring correction as follows: Page 1,first column, line 52', after the word "plug'insert "type"; and secondcolumn, line 52, after the wordandperi od "down," begin a new paragraph;page L, second column, line 514., claim 21+, for "loop" read "looped";line 58, same 'claimrror "hearing" read '-'--bear11 1g and that'the eaidLetters Patent should be read with this correction therein that the samemay conform to the record or the. case in the Patent Office.

si ned and sealed this men-ga of September, A. D. 191m.

Henry Von Arsdale, (Seal) Acting Commissioner -of Patents.

. I CERTIFICATE OF CORRECTIION. Patent na.'2,210,o36. August 6, 194

JAMES- A. mm;

It is neaoy certified that error appears in the printed spemificationvor the above numbered patent requiring correction as follows:Pa'g'e 1, first column, line 52', after the word "plug" insert --type--;and second column, line 32, atter tna wordandperiod "down." pe in a newparagraph; page LL, second column, line 3b., claim 21 for p" d "looped";line 58, same c1aim, or"'hearing" read '-'-bearing and that'the saidLetters Patent should be read with this' correction therein that thesame may' conform to the record 61' the case in the- Patent Office. aSigned and sealed this zhtn'aa of September, A. D. 19!;0.

Henry Van Arsdale, (Seal) Acting Commissioner -of Patents.

